Grade8 Science

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Environmental Science Grade 8 Module 1

WaterWelcome to Unit 1 of Grade 8 Environmental Science. In this unit we

are going to look at water. Our world is full of water. Water is a

useful substance in our lives. Imagine a world without water, can

there be life? We use water for bathing and we all drink water. Canyou think of other ways in which we use water? In this unit we will

look at the properties of water.

What is in this Unit?In this unit you have 6 sections. These are:

Section 1 What is Matter?

Section 2 Change of State

Section 3 Physical and Chemical Change

Section 4 Reaction of Water with Some Metals

Section 5 Effects of Electricity on WaterSection 6 Solutions and Crystals

Read through the learning outcomes carefully, to know what you are

expected to learn at the end of this unit.

Learning OutcomesBy the end of this unit you should be able to:

Fstate the properties of water

Fstate the uses of water

Fstate that water is matter and exists in liquid, solid andgaseous form

Fidentify the changes in states

Fto explain the difference between physical and chemicalchange

Fexplain the reaction of water with some metals and

Fexplain the effect of electricity on water

UNIT

1


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&Learning ResourcesThere are many things you would need if you were going to carry

out all the practical activities in this unit.

We have listed them where we explain the practical activity to you.

Study TimeIn this unit you will probably need to spend at least 6-10 hours to

study the materials. This is only a guideline. You might even spend

more or less hours. If you spend more hours dont worry. What is

important is to complete all the sections and do all the activities

correctly.


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! Activity 1(a)List 10 examples of matter.

Your list is expected to have at least 10 examples.

1.......................................

2...........................................

3....................................

4.......................................

5...........................................

6.......................................................................................

7...................

8.......................................................

9...........................................................................

10.................................................................................................................................

3

Key Ideas

Matter: Anythingthat has mass and

occupies space.

Mass: Is theamount of matterfound in asubstance.


Section 1: What is Matter?You are welcome to Section 1. In the introduction to Unit 1, we talked

about water. Can you remember some of the ways in which we use

water? Take sometime to think. In this section we consider matter,

its nature and its different states. We are surrounded by many forms

of matter. At every moment of our life we are making use of matter.We breathe oxygen from the air. We drink water. Oxygen, air and

water are forms of matter. Iron or wood we use for construction are

examples of matter. Please enjoy studying this section.

Learning ResourcesBefore you start the lesson you need to have the following

a stone

some ice

water a spirit lamp or source of heat

MatterConsider oxygen, air, water, iron and wood which we discussed

earlier. What do you think they have in common? You might have

discovered that all these things can occupy space and have mass. We

can therefore say that matter is anything that occupies space and has

weight.

Before proceeding further, do the following activity to check yourunderstanding of matter.

Check your answer with mine provided at the end of this unit.


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Please note that all things on earth are examples of matter. If you

have not written some of the items suggested in the answer at the

end of this unit, do not worry because, as I said, all things on earth

are examples of matter.

States of MatterMatter exists in three different states. We normally talk about 3 states

of matter:

Solid state


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Key IdeasSolid state: Astate of matterwere particles areclosely packed.

Liquid state: Astate of matterwere particles arenot closelypacked.

Gas state: A stateof matter in whichparticles arefurther apart and

move randomly.

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Liquid state

Gaseous state

Now lets discuss each of these states of matter in more detail.

SolidsOne of the states of matter is a solid. Think of something solid. A

stone is a solid, a chair is a solid. Most solids are hard or stiff.

Solids

Solid things do not change their shape to fill boxes or glasses. If you

put a book in your bag, does it spread out to fill your bag?

...........................................................................

.............................................................................................

The answer is no, the book does not spread out to fill your bag.

Solids are made of tiny particles. The particles of a solid pull on one

another and they are very close to each other. The particles do not

move so much, they only move back and forth. When they move this

way they are said to vibrate.

LiquidsThe particles of a liquid are not as close to each other as particles of a

solid. The particles of a liquid move faster than the particles of asolid. They are also not held tightly together. There is empty space

between the particles. A liquid does not have a shape of its own. It

flows until it fits the shape of the container that holds it. Can you

name some things which are usually in a liquid state?

......................................................................................

..........................................................................

Water, milk, petrol, ink, paint.

Look at the diagram below showing some examples of liquids.

LiquidsGases

Chair

Stone

WoodRail


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You can not see a gas, but it is there. You cannot hold a gas in your

hands.

A gas has no colour or shape, but it is there.

A gas is not a solid or liquid but it is there.

A gas is also a state of matter. Look closely at the picture of a bicycle

tyre and a balloon. They are filled with gases. Can you think of

things that contain gases? There are different types of gases. You cansmell some gases but some gases do not smell at all.

Gases

Particles in a gas are not so close to one another. The particles of a

gas move faster than the particles of either a solid or a liquid. There

is a lot of empty space between the particles of a gas. We can

summarize the characteristics of solids, liquids and gases as follows:

Solids Keep the same shape.

They stay where they are put.

It is not easy to move through a solid.

Cannot be compressed (make small).

Liquids Can take the shape of the container.

Liquids can be poured.

It is easy to move through a liquid.

Gases

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!Activity 1(b)1. Given below are some examples of matter:

Book, stone, oxygen, pencil, orange juice, steam, water, hydrogen, tree, coco-cola.

Write down each item in the correct column. The first one is done for you.

Solid Liquid Gas

Book

Can fill the whole container.

Spread out quickly.

It is easy to move through a gas.

Gases are very easy to compress.

The things mentioned above are used to describe differences betweensolids, liquids and gases. Please note that there are more ways we

can describe solids, liquids and gases.

Before proceeding, complete the following activity to check your

understanding of states of matter.

How did you find the activity? Was it difficult to do? Check your

answer with the answers provided at the end of the unit.


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Mukuka

Section 2: Change of StateIn Section 1 you learnt what matter is and its three states. In this

section, you will learn about how matter changes from one state to

another. What happens when you heat candle wax? What happens to

ice when it is heated? What happens when you put water in a freezer

over night? In this section we will find answers to all these

questions.

Change of StateYou know from Section 1 that matter exists in three states:

Solid state

Liquid state

Gaseous /vapour state

In this section you are going to observe some changes that happen tomatter when it is heated or cooled. You know that water is matter in

liquid form. Water can also exist in other states such as solid (ice) and

gas (vapour).

You will also observe from the experiments in this section that water

can change from one state to another when we heat or cool it. Now

let us find out from this experiment how water or candle wax can

change from one state to another. Our two friends Sibeso and

Mukuka will join you in doing this experiment.

Practical Activity 1:What happens when you heat wax?

I will need the following materials: a beaker a stirring rod

a thermometer a source of heat - stove or Bunsen

burner

candle wax

Sibeso: What will you do next?

Mukuka:I will put some candle wax in a beaker over asource of heat. I am going to use the stove.Here is a picture showing the beaker on a tripodstand over a Bunsen burner. This is what you woulduse in a science laboratory.


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Figure 1.2

Mukuka:Now I am going to heat the wax gently on the stove.

Sibeso: Be careful not to burn yourself!

Mukuka I will put some candle wax in a beaker over asource of heat. I am going to use the stove.Here is a picture showing the beaker on atripod stand over a Bunsen burner. This is whatyou would use in a science laboratory.

Now here is a question for you:

What do you think happens to the wax in the beaker

as Mukuka heats it? Write your idea in this space..........................................................................1. The solid wax slowlydisappearsand turns into

liquid. it has changed state from solid to liquid.

Now Sibeso is going to do another practical activity.

This time you are going to find out what happenswhen we heat ice.

Practical Activity 2:

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Source of heat

Wax

Beaker

Thermometer


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What happens when you heat ice?

I am going to use the following materials: a beaker a stirring rod

a thermometer a source of heat some ice

Mukuka:Tell us what you are going to do.

Sibeso: I will put some ice in a beaker on the tripodstand. You can see a drawing in Figure 1.3

below. I will also put the thermometer in the

beaker. Figure 1.3

Sibeso: Next I will heat the ice in the beaker gently but I

am using a stove. I am going to leave thethermometer in the beaker for 10 minutes.

Mukuka:What did you discover Sibeso?

Sibeso: The temperature reading before heating was about0C or below. As I heat the ice it slowly disappearedand turns to water.

When I continued heating, the temperature of thewater rises and the water turns to water vapour andrises out of the beaker as steam.

So now you have seen that when you heat ice it first changes state

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Sibeso

Source of heat

Ice

Beaker

Thermometer


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from solid to liquid. As you continue heating the liquid changes to

water vapour or steam.

Now let us do another practical activity. This time you are going to

observe what happens when ice is left in the beaker at room

temperature. In this case we are not going to heat the ice.

Practical Activity 3:What happens when you leave ice in an openspace at room temperature?

I will need the following materials:

A beaker, a thermometer and ice

This is what I am going to do:

I will put some ice in a beaker place it on thetripod stand as shown in figure 1.4 below.

Figure 1.4

I will then place the thermometer in the beaker.

I will leave the ice and thermometer in thebeaker for some time.

Sibeso: Now mukuka answer the following questions:

1. What happens to the ice after some time?.................................................................................

2. Is there any change in the thermometer

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Mukuka

Tripod stand

Ice

Beaker

Thermometer


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Sibeso

reading?....................

3. What did you observe on the outside of thebeaker?....

Mukuka : Here are the answers:

1. Solid ice is slowly turning into water.

2. There is no change in the thermometerreading.

3. Some water droplets have formed outsidethe beaker.

Now you can read the information below to help you understand

what happened to wax and ice in experiments 1, 2 and 3 this Section.

FMelting and Melting PointYou may have noticed that as you heat wax and ice they change, to

form a liquid. This change of wax or ice is called melting. When

the temperature of ice is raised above 0C, it melts to form water. All

solids turn to liquids when they reach their melting points. Now lets

see what happens to temperature of a solid as it melts.

FWhat Happens to the TemperatureDuring Melting?

You may have observed from the practical activity that we need to

keep heating until all the solid melts. The temperature stops rising

and stays at the same point.

Now let us find out what happens when you heat water. To do this

we are going to do the practical activity below:

Practical Activity 4:What happens when you heat water?

I will need the following materials :

a beaker a tripod water

a source of heat.Sibeso: This is what Iam going to do:


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Source of heat

Beaker

Steam

Water

Tripod stand

I will fill half of the beaker with water. ThenI will mark the level of water in the beaker. Iwill then place the beaker on the tripod stand

as shown in figure 1.5.Figure 1.5

I will heat the water in the beaker.

I will Continue heating it until it starts boiling. I will let the water boil for at least 10 minutes

and then stop heating.

Mukuka:Sibeso, have you finished doing the practicalactivity?

Sibeso :Oh, yes. I have !

Mukuka:That's good. Now answer the followingquestions:

1. What happens to the water as you heat it?

......................

2. What do you see on the surface of the water inthe beaker as the water boils?................

3. Now look at the level of water, does it

change?


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..................

4. Give a reason for the change in the water level..........

.........Sibeso: Here are the answers:

1. As I started heating the water small bubblesstarted forming in the beaker.

2. As the water boils more bubbles are formedand steam starts coming out of the beaker.

3. The level of water starts dropping as the wateris boiled for some time.

4. The level drops because evaporation has takenplace.

We now discuss in more detail what happens to particles of water

when we heat it.

FWhat happens when water isboiled?

When we heat water the particles move about more quickly. Some of

the particles move very fast and they break out of the surface of the

water in the form of water vapour or steam, which spreads in the air.

This process is called evaporation. Particles of water vapour (gas)

arenot close to each other. They are free to move about. These

particles can spread to fill any container. They are separated from

each other by a lot of space.

What happens to the temperature

When water is boiled?Can you remember what happens to the temperature when it reaches

its melting point? Write your answer in the space below:

..............................................................

..................................................

The temperature stops rising and stays at the melting point. The

same thing happens when you heat water. When water reaches its

boiling point the temperature stops rising and stays at the boiling

point.

Do you know the boiling point of pure water?

......................................

..................................................

F


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Mukuka

The boiling point is 100C.

FExplaining EvaporationWe saw from the activity that when water reaches its boiling pointthe particles break free from each other and mix with other particles.

The particles get a lot of energy and they move about very fast. The

particles then move away from the surface of the water in form of

water vapour which spreads in the air.

In the practical activity you saw that the level of water dropping as

you continued boiling it. Where did this water disappear to? Of

course it evaporated. After washing our clothes we hang them in the

sun to dry. Do you know what happens to the water in the wet

clothes?Figure 1.6

Clothes drying in the sun

The water evaporates leaving the clothes dry. Let us now find out

what happens when we cool water. We will now try the practical

activity below. Our two friends will do the activity for you. Read and

follow what they do.

Practical Activity 5:What is the effect of cooling water?


A refrigerator or deep freezer

A beaker with cold water

Sibeso: Mukuka, what are you going to do now?Mukuka:I will do the following:

Half fill the beaker with water put the beaker in thefreezer of the refrigerator. Leave the beaker in the


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Sibeso

freezer until the following day.

Sibeso: Mukuka answer the following questions now:1. What happens to the water in the beaker?

.......

.....2. How does the beaker feel like when you

touch it?......

......

Sibeso 1. I noticed that the water in the beaker hasturned into ice.

2. The beaker feels very cold as I touch it.

FExplaining FreezingWhen you cool water it turns into a solid (ice). This process is called

freezing or solidification. Freezing or solidification happens when a

liquid loses heat. The temperature at which a liquid changes to a solid

is called its freezing point. The freezing point of pure water is 0C.

FCondensationNow let us look at what happens when you cool steam. Our two

friends Sibeso and Mukuka will work with you in the followingpractical activity.

Practical Activity 6:Effect of cooling steam


A source of heat (a brazier)

A kettle

A bottle

A beaker Water

Sibeso: I am going to set up the apparatus as shown infigure 1.6 below. Then will do the following :

Fill half of the kettle with water.

Place the kettle with water on a brazier.

Heat the water gently until it starts to boil.

Hold the bottle close to the kettle sprout

(Mouth of the kettle)as shown in figure 1.7.


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Brazier

Drops of water

Cold water bottle

Steam

Sprout

Kettle

Beaker

Place a beaker below the bottle.

figure 1.7Condensation

Mukuka:Sibeso, now answer the following questions :1. As the water boils, what do you see

coming out of the mouth of the kettle?....

2. What do you see on the surface of thebottle?

..

Hold the bottle in the same position for

sometime.

3. What is dropping into the beaker belowthe bottle?

Sibeso :This is what I saw:1. As the water started boiling steam or

water vapour started coming out of the

mouth of the kettle.2. Small drops of water started forming on the

surface of the bottle with cold water.3. Drops of water collected in the beaker below

the cold water bottle.

FWhat have you learnt from this


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practical activity?We have seen that water can change from one state to another. When

you boil it changes to gas in the form of water vapour or steam. If

you cool the steam (water vapour) it changes back to liquid water.

This change of water from gas to liquid is called condensation. The

processes we have discussed above can be summarised as shown in

Figure 1.7. Is it possible for a solid to change straight to a gas? Yes, it

is. Let us find out from this practical activity. Our two friends will

again do the activity for you.

Practical Activity 7:

I will need the following materials: A test tube

A test tube holder

Crystals of iodine

A source of heatFigure 1.8

Sublimation

Mukuka:I am going to set up the apparatus as shown infigure 1.8. Then I will do the following:

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Ice WaterWaterSteam

SteamIce WaterHeat heat

Cool

Heat heat cool

Figure 1.7


Mukuka

Purple smoke

Test tube holder

Source of heat

Iodine crystals

Test tube


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Place a small quantity of iodine crystals in a

test tube. Hold the test tube in a holder Heat the bottom of the test tube gently for a

few minutes.Sibeso: Mukuka, have you finished doing the practical

activity?

Mukuka:I have finished. It was very interesting !Sibeso: Good ! then answer the following questions:

1. What happens to iodine in the testtube?

2. What do you see in the upper part of

the test tube?..

3. What happens to the quantity of iodineat the bottom of the test tube?..

What happens when you heat iodine?

These are the results I got:

1. There was only small amount of iodine remainingat the bottom of the test tube.

2. We have seen that the iodine changed from solid

to gas without becoming a liquid.3. There was only a very small amount remaining at

the bottom of the test tube.

This change in which a solid turns directly into a gaswhen heated is called sublimation. Sublimation is alsoused to describe the change of state from gas to

solid when a gas is cooled.

1. The iodine crystal at the bottom sublimes andchanged its colour to purple.


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2. A purple smoke is seen coming out the test tube.

FWhat can you learn from thepractical activity?

After heating the iodine crystals the shiny and bright crystals gave a

purple smoke. The upper part of the test tube had some crystals of

iodine when the test tube was cooled. Examples of substances that

sublime include Iodine, Solid Carbon dioxide and Ammonium

Chloride. The change of state of matter can be summarised as shown

below.

Figure 1.9

Change of state of matter

Now try this activity to see how much you have learned

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Sublimation

SolidificationMelting

Solid

Liquid

EvaporationHeat

Gas

CoolCondensation

Sublimation

Condensation

Heat Cool


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!Activity 21. Name the three states of matter.

........

2. Distinguish between the three states of matter in terms of their particles.

.....

.............................

.....

3. In your own words explain the following processes:

(A) Melting ....................................

(b) Evaporation .....

(c) Condensation .

(d) Sublimation

4. Give two examples of substances that undergo sublimation.

(a) ...........

(b) ......


Check your answer with the answers provided at the end of thisunit.


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Key Ideas

Irreversible :means hat asubstance cannotbe changed backto its originalform.


Section 3: Physical and ChemicalChange

Welcome to Section 3. In the last two sections you learnt about the

changes in the states of matter. You now know that matter can

change from one state to the other. These changes can either bephysical or chemical. In this section we are going to learn more

about physical and chemical changes.

FPhysical ChangeA physical change is one which does not produce any new substance

and the change can be reversed.

I am sure you have all seen ice. Ice is one of the common substances

found in your area. Now, when you heat ice as a solid, what

happens? Of course ice will change state from being solid to liquid.

This changeof state is called melting. When ice melts into a liquid,

is there any new substance formed? No new substance is formed.

Suppose, we put water in a freezing compartment of the refrigerator

for at least 24hours, what will happen to it? The water turns to ice,

no new substance is formed as the water can be turned back to ice on

cooling it in the refrigerator. Therefore the melting of ice and the

freezing of water are examples of a physical change. Another

example of a physical change is dissolving. You are familiar with

sugar or salt dissolving when stirred in water. Here again no new

substance is produced. Can you think of any physical change that

commonly takes place around your home? Now lets look at another

type of change.

FChemical ChangeThis is just the opposite of physical change. A chemical change is a

change which always produces new substances. A chemical change

is irreversible. By irreversible we mean that this substance cannot be

changed back to its original form.

Now let us proceed with the following investigation. Sibeso and

Mukuka will do this demonstration for you. Please follow what they

do, carefully.


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Mukuka

Practical Activity1: Showing a ChemicalChange

I will need the following materials: Match box

Matches

A white plain sheet of paper

Mukuka:This is what I am going to do :Strike a match and light a piece of paper. I will

then let it burn for a while and blow it off.

Sibeso: Mukuka, you can now answer the following questions :1. What happens to the colour of the

paper?2. Does it represent a physical change or a

chemical change?

...............3. Justify your answer in (2)?

..

This is what I observed:

1. When the paper was burnt, it turned black, theblack substance is called ash.

2. This represents a chemical change because ash isa new substance.

3. This ash cannot be reversed to paper.

Other examples of a chemical change include burning of wood,

reaction between magnesium and oxygen, reaction of water and

calcium.

At this stage we can say that in a chemical change, new substancesare formed but in a physical change, no new substances are formed.

I hope you have now understood the difference between physical

and chemical changes.


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!Activity 31. Below are some statements describing physical and chemical changes. Write

either P (for physical change) and C (for chemical change) next to thestatements.

(a) Boiling water

(b) Boiling an egg ..

(c) Melting of ice

(d) Chewing a bubble gum

(e) Burning a piece of wood .

2. List three (3) other physical changes.

(a) ...

(b) ...

(c) ...

3. Explain the difference between chemical and physical change.

........


Now do the following activity to check your progress.

I hope you have now understood the difference between chemical

and physical changes. Now compare your answers with mine at the

end of this unit.


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Sibeso

Section 4: Reaction of Water withSome Metals

Welcome to Section 4, I hope you have now understood the

difference between physical and chemical changes in section 3. Now

you are going to move a step forward and study more on how somemetals react with water. Where you live are there any metals

around? What about in your house, are there any objects made of

metal? What happens when water comes in contact with metal?

What about when you go to collect water from the well or river or

tap, do you use a plastic or metal bucket? If you use a metal bucket

does the water react with the metal bucket? If so how can you know

that the metal bucket is reacting with water? Well, this section will

look at what types of metals react with water.

Learning Resources Calcium metal

Magnesium ribbon

Iron fillings

Copper fillings

Pair of tongs

Clamp stand

Six test tubes

Test tube rack

Beaker

Burner Match stick

To find out if some metals react with water. Join Sibeso and Mukuka

as you carry out several practical activities. We will start by looking

at how at what happens when calcium reacts with water.

Practical Activity 1:Reaction of calcium and water


Water

Test tube

Burner

Calcium Pair of tongs/spatula

Mukuka:You will need to be very careful when pickingthe metals. Use a spatula for the calcium; donot use your fingers because it is corrosive to

the skin. Please be careful. If it comes in


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Beaker

Water

Calcium

contact with your skin, wash your hands carefully.

Sibeso: Thank you Mukuka for the warning, To carry out this

practical activity iwill set up the materials as shownin figure 1.10. I will then do the following :

Get a test tube and half fill with water.

Using a pair of tongs or spatula get a piece of

calcium and drop it into the cold water.

After 3 minutes get the same beaker and heat

the water with the burner.

Figure 1.10

Reaction of calcium and water

Mukuka:Sibeso, you can now answer the followingquestions:

1. What happens to the calcium metal whenit is in cold water?

2. (a) What can you say about the speed of thereaction when you heat water?(b) What is the difference in the two reactions?

These are the results I got:

1. Bubbles are produced; this shows that a

reaction is taking place.


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Mukuka

2. (a) More bubbles are produced at a faster rate.

(b) Reaction of Calcium in warm water is fasterthan the reaction of calcium with cold water.There are more bubbles produced in warm water

than cold water.

FWhat can you learn from thispractical activity?

You have learned that calcium can react in both cold and warm water.

The difference in the reaction is that Calcium reacts faster in warm

water than cold water. Now lets try another investigation, this time

we want to see what happens when a metal: magnesium is mixed

with water. Now let us move to practical activity 2. Sibeso andMukuka will again do the practical activity with you.

Practical Activity 2:Reaction of Water with Magnesium


Test tube

A pair of tongs Water

Source of heat

Mukuka:I am going to set up the apparatus as shown infigure 1.11a. Then I will do the following :

Get a test tube and half fill the test tube withwater.

Using a pair of tongs carefully get the magnesium

ribbon and gently put in the test tube of water.Look at the diagram below. Make sure you havearranged your apparatus accordingly.


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Figure 1.11(a)Reaction of water with magnesium

Observe the reaction.

After 3 minutes get the same test tube withmagnesium ribbon then heat gently till it boils.

Figure 1.11(b)

Reaction of water with magnesium

Sibeso: Mukuka, you can now answer the followingquestions :1. What is happening to the magnesium ribbon

in the test tube of cold water?............

2. What is happening to the reaction ofmagnesium in warm water?.......

3. What can you say about the reaction ofmagnesium in cold and warm water?

This is what I observed:

1. No reaction is taking place.2. Few bubbles are seen hence reaction is taking

place.3. Well magnesium does not react in cold water but

it reacts in warm water.

Let us now look at another practical activity.

Test tubeWater

Test tube holder

Magnesium ribbon

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Test tubeWater

Source of heat

Test tube holder

Magnesium ribbon


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Practical Activity 3:Reaction of Water and Iron


1 test tube water

iron fillings

Spatula

burner

Figure 1.12Reaction of water and iron

Sibeso: I am going to set up the apparatus as shown

in figure 1.12. Then I will do the following :

Get a test tube and half fill it with water.

Using a spatula collect the iron pieces

and put then gently into the test tube. Observe thereaction carefully.

After 3 minutes, gently heat the test tube till thewater starts boiling.

Mukuka:Sibeso, you can now answer the following questions :

1. What reaction can you see when you put piecesof iron in cold water?....

2. What reaction can you see when you put iron inwarm water?

3. What can you say about the reaction of iron incold or warm water?

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Test tube

Test tube holder

Water

Iron fillings

Sibeso


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Mukuka

Sibeso: This is what I observed:

1. No reaction is taking place when I placed ironpieces in a test tube of cold water.

2. No reaction is taking place when I placed ironpieces a test tube of warm water.

3. There is no reaction with either cold water orwarm water.

FReaction of iron with waterWe have learnt that iron does not react in either cold water or warm

water.

Let us now look at another activity. This time we will find out what

happens when water mixes with copper.

Practical Activity 4:Reaction of Copper with Water


1 Test tube

Water

Burner

Copper

Pair of tongs or spatula

Mukuka:I am going to do the following :

Get a test tube and half fill it with water, Using a pair of tongs collect pieces of the copper

metal and put them in the test tube of cold water asshown in Figure 1.13 (a).


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Figure 1.13 (a)

Set up the apparatus as shown in figure 1.13 (b).

Figure 1.13 (b)

Now heat the test tube for 3 minutes till it starts boiling.

Sibeso: Mukuka, you can now answer the followingquestions:

1. What happens to the copper in cold water?.

2. What happens to the copper in warm water?....

3. What can you say about the reaction of copperin cold or warm water?

..

This is what I observed:1. There was no reaction when you mixed cold water

with copper in the test tube.

2. There was no reaction when you mixed warmwater with copper in the test tube.

3. Copper does not react in either cold water orwarm water.

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Test tube

Test tube holder

Copper metal

pieces

Water

Test tube holder

Test tube

Source of heat

Water

Copper metal pieces


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FWhat can you learn from theseactivities?

Let us see what was actually happening in these practical activities

and the conclusions we are going to draw from them.

Firstly you noticed that some metals can react in both cold and hot

water. Can you list which metal reacted in cold and hot water?

.. ............ calcium reacted in both cold and hot water.

Some metals could not react in cold water but only hot water, which

metal is this? It is magnesium.

On the other hand some metal could neither react in cold water or

hot water. Which metals are these? .................. and Yes the two metals are iron and copper. But there

is some thing about iron you must know, it does react with water if

there is oxygen in the water. When you look at some metal buckets

or cups or dishes you use for collecting water you will notice a

brownish substance on them. This is called rust. That is a reaction

between iron and water in the presence of oxygen.

Calcium reacts faster in cold and hot water than these other metals,

what can you conclude? Well you can say Calcium is more reactive

metal than magnesium, iron and copper. Magnesium is also morereactive than iron and copper. Copper is the least reactive metal.

Another metal which reacts with water at a faster rate is potassium.

Its the most reactive of all metals.

Because of the way these metals react they are put in what is referred

to as a reactivity series. A series is a sequence or line up in which

metals are arranged according to how fast the react with water. Look

at the reactivity series below and study it carefully. The list starts

with the most reactive and ends with the least reactive metal.

Potassium most reactive

Calcium

Magnesium

Aluminium

Zinc

Iron

Lead

Copper

Gold - least reactive


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Mukuka

Clamp stand

Test tube

Beaker

Water

Calcium

Now that you have studied how metals react with water and how

they are arranged in the reactivity series from the most reactive to the

least reactive, we are going to identify what is produced at the end of

the reaction.

Well first you will need to carry out another practical activity.

Practical Activity 5:Reaction of Calcium with Water


A beaker

Test tube

Clamp stand Calcium

Figure 1.14a

Reaction of calcium with water

Mukuka:Iam going to do the following :

Set up the apparatus as shown in figure 1.14a

Using pair of tongs I will collect enough some pieces

of calcium and put it in the beaker.

Quickly cover the calcium with a test tube as shownin the figure 1.14a.


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Clamp stand

Beaker

Water

Calcium

Gas

Figure 1.14b

If the reaction is slow I will heat the water, I willalso make sure I have enough calcium.

When all the water has been displaced or removed bythe gas collected in the test tube,1 will remove thetest tube while its mouth is still in water trough thenclose the mouth immediately with my finger before Iremove it from the water.

Light a wood splint or match stick, and thenintroduce the burning splint to the gas inside the testtube quickly.

Figure 1.14c

Sibeso: Mukuka, its now time for you to answer the followingquestions:

1. What happens to the water as bubbles arecollected in the test tube?

.........

2. What happens when the burning splint ormatch stick is introduced to the gas collected?........................

Mukuka:1. Gas displaces the water in the test tube andwater turns milky

2. Flame of the burning splint is put off with apop sound.


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FWhat can you learn from thispractical activity?

You have already learnt how calcium reacts with water. Well when it

reacts a gas is produced. The gas produced is hydrogen. Since anew product is produced this is a chemical change. But how can you

know that it is hydrogen gas that was produced? Think about it.

Well can you remember what happened when you introduced a

burning splint to the gas? What happened?

.................

.................................................

The flame was put off with a pop sound. The test identity of

hydrogen is shown by putting off a burning splint with a pop sound.

How can you show the reaction between water and the metals we

have studied? Study the word equation below.

Metal + Water Metal hydroxide + hydrogen

e. g. Calcium + Water Calcium hydroxide + Hydrogen

You notice that another substance is produced apart from hydrogen.

This is calcium hydroxide.

Well calcium hydroxide is a solution that is formed when calcium

and water reacts. Calcium hydroxide is an alkaline solution. How

can you identify an alkaline solution? Well you use a special red

paper called red litmus paper. When you dip a red litmus paper in

this solution it will turn blue. This will always happen to any

solution that is an alkaline.

Remember that when most metals react with water hydrogen gas is

given off plus the hydroxide of that metal. For example in the aboveexperiment the hydroxide of calcium is calcium hydroxide, in fact

the water turns milky because of the presence of calcium hydroxide.


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!Activity 41. (a) Arrange the following metals in the reactivity series starting with the least.

Zinc ....Iron ....

Magnesium ...

Lead ...

Aluminium ...

(b) Write a word equation of the reaction of magnesium and water?

........

(c) What gas is produced in the equation you have written above?

............

(d) What test is used to identify this gas?

........................................................

Now do the activity below to check your progress so far.

How did you find this activity? Check for the answers to this

exercise at the end of this unit. If you found any part difficult go back

and re-read the parts you did not understand well.


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Section 5: Effects of Electricity onWater

Welcome to section 5. I hope you enjoyed studying the previous

sections. In this section you will learn about the effect of electricity

on water. In the previous section you learnt that water reacts withmetals such as calcium and magnesium. Now what do you think

could be the effect of electricity on water? You will learn more about

this in this section. In order to find out the effect of electricity we will

start by doing the practical activity below. Our two friends Sibeso

and mukuka will join us as we do the activity. Please read and follow

all the very carefully.

Practical Activity1:To Find Out the Effects of Electricity on Water

I will need the following Materials:

Two carbon rods

Medium sized test tubes

Connecting wires

A switch

Wood splint

Two beehive shelves

One 6 volt battery

Water and dilute hydrochloric acid

Mukuka:This is what I am going to do :1. I will arrange the apparatus as shown in the

diagram below.

Figure 1.15Effects of electricity in water

I will close the switch and carefully observewhat happens

I will now add a few drops of the dilutehydrochloric acid and carefully stir the water.

37

Environmental Science Grade 8 Module 1Key Ideas

Electrolyte: Is asolution that canconductelectricity.

Mukuka

Bulb

Gas collecting

Gas bubbles

Trough

Test tube

Electrode (anode)

Battery

6V

Electrode (cathode)

Beehive shelf

Switch

Gas collecting


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Leave the set up for some time in order forthe gases to collect.

Now carefully remove one of the test tubesoff its electrode making sure that the gas doesnot escape. Introduce a burning splint to the

mouth of the test tube. Remove the other test tube as before.

Quickly introduce a glowing splint.

Sibeso: Be careful as you handle dilute hydrochloric acid asit can burn your skin. Mukuka now answer thefollowing questions :

1. What do you observe at the two electrodes whenthe switch is closed?....

2. What do you observe at the electrodes afterdilute hydrochloric acid was added?.......

3. After some time (15 minutes) what do youobserve with amount of gases collected atthe electrodes?

....4. What do you observe when you put the burning

splinter in the first test tube?

........

5. What do you observe when the burning splint isintroduced in the second test tube?............

6. What can you say about the nature of gasescollected?

............

Mukuka:I observed that:

1. When the circuit was closed before adding thedilute hydrochloric acid, there were no bubblesare produced at the electrodes.


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2. After adding the acid bubbles started beingforming around the electrodes.

3. After about 15 minutes quite a lot of gashad collected in each tube. There was more

gas produced in one tube than the other.

4. When a burning splint was introduced in the testtube with more gas it was put off with a popsound.

5. When I introduced a glowing splint in the testtube it was re-lighted and burnt more brightly.

FWhat can you learn from this practicalactivity?

When electricity is passed through acidified water, gases are

produced. Electricity can not pass through pure water because it is a

bad conductor of electricity. Dilute hydrochloric acid is added to the

water to make it conduct electricity.

When a dilute acid is added to water, it becomes an electrolyte. An

electrolyte is a solution which will conduct an electric current and be

decomposed by it. To decompose is to break down into smaller

parts. Electricity decomposes (splits) water into simpler particles.Therefore this decomposition of an electrolyte is known as

electrolysis. How are you coping with this new information? This

splitting of water into simpler particles, is it a chemical or physical

change?

......................

It is a chemical change. The gases are produced at the electrodes. An

electrode is a plate or rod which conducts electricity in and out of an

electrolyte. These electrodes can be made of metals like platinum,

zinc,copper etc or a non metal like carbon.

In your experiment you connected one of the electrodes to the

positive terminal and the other to the negative terminal. These

terminals are made of metal rods or plates. The one that was

connected to the positive terminal is called the Anode. The one

connected to the negative terminal is called the Cathode.

One of the gases put off a burning splint with a pop sound, it is

hydrogen. The other gas relit a glowing splint, it is oxygen. These

two observations are the identity test of the gases respectively.


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Now try this activity to check your progress.

How did you find the activity? Was it easy? Now compare your

answers with mine at end of the unit.

40


!Activity 51. The diagram below shows an experiment used to produce two gases by

passing an electric current through an electrolyte.

Electrolysis

Figure 1.16

a. Suggest the electrolyte used in this experiment.

...........

b. What is the name of the process of decomposing a substance using an

electric current?........................................

............................................................................................................................

c. Name the gas that would be collected in test tube A.

..............

d. What is the identity test for the gas that would be collected in test tube B?

..........

e. Which test tube would contain a larger amount of gas at the end ofthe experiment?

..............

f. What is the use of the gas collected in test tube A?

...............

Electrode (cathode)

Trough

Test tube

Electrode (anode)

Battery

6V

Test tube

Electrolyte

Switch

BAMore gas

Gas


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41


Key Ideas

Solution: this isformed when asolid dissolves ina solvent.

Crystals: solidswith a definiteshape formedfrom a solution ofits solute.

Mukuka

Section 6: Solutions and CrystalsWhen you add small amount of sugar to water the sugar disappears.

When the sugar disappears, it becomes a sugar solution. In this case

sugar is soluble in water because it forms a solution which is a sugar

solution. Is this a chemical or physical change?

In science we use some general words to describe the sugar and

water. The sugar is called the solute and the water is called solvent.

In this section we are going to look at solutions and crystals in

general.

FSolutionsRemember that when you add small amount of sugar to water, thesugar disappears. The disappearing of the sugar is called dissolving.

When sugar dissolves in water it forms a solution. In science the

sugar is referred to as a solute and the water as a solvent.

Note that sugar dissolves faster in hot water than cold water. When

we add more sugar to very little water, the sugar will not dissolve

any more. In science we say the sugar has been saturated. The

solution is now called saturated solution. Let us find out more about

this in the following investigation.

Practical Activity 1:What Materials Dissolve in Water?


Salt

Sugar

Mealie meal

Sand 4 beakers with water

Stirring rod or spoon

Mukuka:I am going to do the following :

Add a teaspoon of sugar to the water in thefirst glass and label it sugar.

Add a teaspoon of salt to another glass withwater label the beaker salt.

Add a teaspoon of mealie meal to the thirdglass and label it mealie meal.


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Add a teaspoon of sand to the fourth glassand label it sand.

Sugar salt mealie meal sand

Figure 1.17

Sibeso: Mukuka, now answer the following questions:

1. Which of the solids seem to disappear?............

2. Which solids can you still see?

..........

Mukuka:These are the results I got:

1. Sugar and salt disappeared after stirring it in

water for a few minutes.

2. Solids like sand and mealie meal did notdisappear instead they collected at the bottomof the glass of water.

FExplaining SolutionsYou saw from the practical activity that sugar and salt, disappeared

or dissolved when it was stirred in water. We can say sugar or saltare soluble in water (they are able to disolve). The mixture of water

and salt or sugar is called a solution.

FA saturated SolutionIf you keep adding sugar to a glass of water at first it will dissolve.

What do you think can happen if you keep adding more and more

sugar? The sugar will reach a point where it will no longer dissolve

in water. The more sugar you add you will observe that there will betoo much sugar for the water to dissolve, when this happens we can

say you have made a saturated solution of the sugar.


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Mukuka

FSeparating MixturesWe have discussed that salt can easily dissolve in water. What about

Sand can it easily dissolve in water?

................................................

Sand cannot easily dissolve in water. We have see that we can mix

salt and sand with water, yet they cannot be separated the same way.

How can you separate a mixture of bean and maize seeds?

...........................

...............................................

You can separate these two by sorting them by hand, you can do this

by placing bean seeds in one pile and maize seeds in another pile.This is a fairly easy way of separating mixtures. Is it easy to separate

salt from water?................................

No, it is not easy to separate salt and water using our hands. These

mixtures are called solutions, they have to be separated using other

methods. Now do the practical activity below in which we will

investigate how to separate a mixture of sand and salt in water.

Practical Activity2:

Separating a Mixture of Salt, Sand in Water


Two beakers A stirring rod Clamp and stand Bunsen burner An evaporating dish Sand Water Filter funnel Filter paper

Mukuka: I am going to do the following : Place 2 teaspoons of sand and 2 teaspoon salt

in a beaker. Mix the sand and salt well using a stirring rod.

Add about 50ml of water to the mixture of

sand and salt. Stir the mixture of sand, salt and water in


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the beaker with a stirring rod,

Sibeso: Mukuka, now answer the following questions:

1. What happens to the sugar and salt afterstirring?

Figure 1.18

Set up the apparatus as shown in figure 1.19below.

Figure 1.19

Filtration

...

.

Mukuka: I will continue with the practical activity by doingthe following:

Place the beaker with the mixture on the burnerstand and heat it gently while stirring themixture with a stirring rod.Fold a piece of filter paper as shown below in

figure 1.19 below and place it in a funnel.

44


First fold

Second fold

Funnel

Filter paper

Third fold

Beaker

Salt solution

and sand

Residue

Beaker

Liquid

Filter paper


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Now pour the hot liquid onto the funnel.

Please make sure that any liquid that passes

through the filter paper is collected in the beaker asshown in the diagram.

Pour the liquid that has collected in beaker below thefunnel onto the evaporating dish as shown in figure1.20 below:

Figure 1.20

Put the dish on a burner and heat theliquid until all the water evaporates.

Sibeso :Mukuka, you can now answer the following questions

1. What remained on the filter paper?....

2. Describe the liquid that collected in thebeaker after filtering.

..

What is left on the evaporating dish as all thewater evaporates?......................

3. When you stirred the white salt and brown sandin water, the white salt dissolved in water leavinga brownish substance which later settled at thebottom of beaker.

4. After pouring the mixture of sand and salt a

brownish substance (sand) remained on the filterpaper.

45


Steam

Filtrate

Stand

Source of heat

Evaporating dish


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5. A clear liquid collected in the beaker at thebottom of the funnel.

6. Salt crystals were left on the evaporating dishas the water evaporates.

FExplaining FiltrationWhen a mixture of salt, sand and water is poured on the filter paper

placed in a funnel, sand is separated from salt using a process called

filtration. The salt solution is able to pass through the small holes in

the filter paper because salt particles are very small. The sand

particles cannot pass through the holes because they are too big.

Filtration is usually used to separate the solid and liquid parts of a

suspension. A suspension consists of solids that cannot dissolve in

water for example sand. The liquid part is called the filtrate. Thesolid that remains on the filter paper is called a residue.

FSoluble and Insoluble MaterialsThe practical activity shows that not all substances can dissolve in

water. Those that dissolve in water like salt are said to be soluble in

water, those that do not dissolve are referred to as insoluble. Can

you write 2 examples of solids that are soluble in water?

1..

2..................

Did your answer include salt and sugar? There many substances that

is soluble in water. Salt and sugar are some of the common

examples. Now write 2 examples of solids that cannot dissolve in

water.

1....................

2........................

Did your answer include sand, stones or mealie meal? Any way

there are more substances that cannot dissolve (not soluble) in water

in addition to the ones I have suggested above.

FCrystalsWhen saturated solution is cooled, some of the solute comes out of

solution as a solid called a crystal. This process is called

crystallisation.


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Sibeso

Now let us do the practical activity below.

Practical Activity 3:Making Crystals of Copper II Sulphate


Copper II sulphate

Water Spoon Trough Filter paper Stirring rod Two beakers

Thermometer

Sibeso: Iam going to do the following:

Put 50ml of water in a beaker. Add a little amount of copper II sulphate using a

spoon.

Stir the mixture well until all the copper II sulphatedissolves.

Keep adding a little copper II sulphate at a time

until no more will dissolve. Using a filter paper filter the solution into another

beaker. Leave the saturated solution over night.

Mukuka:Sibeso, now answer the following questions:

1. What do you see in the beaker the next day?...

2. Now pick the largest crystal and suspend it by athread as shown in figure 1.23 below.

Look at the crystal each morning for 3 days.

3. Record what you see after 3 days as shown infigure 1.23 below...


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Copper sulphate

solution

Crystal

!Activity 61. What is a solution?

...............................

.......

2. What do you call a solid that dissolves in liquid?

...

...

3. What name is given to the process by which crystals are formed?......

.......

4. What do you call a solution that can not dissolve any more solute at a giventemperature?

.......

......

Figure 1.23Growing a copper sulphate crystal

1. Next day I saw that the crystal is growing.

2. The crystal grew bigger and had definite shapeor pattern.

What can you learn from this activity?When the saturated copper sulphate solution was left for a few days,

particles came out of the solution. The crystal grew slowly over the

five days. The crystal despite its growing bigger kept the same shape

or pattern. When a saturated solution is cooled solid crystals are

formed this process is called crystallization. Some of the common

crystals include

Salt

Sugar

Now try this activity to see how much you have learned.

How did you find this self marked activity? Was it easy? If not,

please do not panic just re-read the section and make sure you

understand the subject matter before proceeding to the next part.You will find the answers at the end of this unit.


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Unit Summary

Matter is defined as anything that occupies space and

has mass.

Matter exists in three different states namely solid,liquid and gas.

In a physical change, no new substances produced and its

reversible.

In a chemical change a new substance is formed and it not

reversible.

Matter changes state when it is heated or cooled.

The processes that take place with during the change of

state are melting, boiling, solidification, evaporation andsublimation.

The tiny particles in solids are closely packed together.

The tiny particles in liquids are further apart.

In gases, the tiny particles are still further apart.

Dilute acid is added to water to make it a good electrolyte.

RAnswers to Activities in this Unit

Activity 1(a)

Solid Liquid Gas

1. Book 5. Water 8. Oxygen

2. Stone 6. Soft drink 9. Nitrogen

3. Metal

4. Brick 7. Orange juice 10. Hydrogen

Activity 1 (b)


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Solid Liquid Gas

Book Water Oxygen

StoneSoft drink Nitrogen

Metal Orange juice Hydrogen

Brick

Activity 1 (b)

Figure 1.24

Activity 2

1. Solid, liquid, and gas

2. In solids particles are closer to each other.

In liquids particles are a little further apart.

In gases particles are free to move about since they are

further apart.

3. (a) Melting is when a solid changes to liquid

(b) Evaporation is when a liquid changes to vapour

(c ) Condensation is when a vapour (steam) changes to liquid.

(d) Sublimation is when a gas changes directly into solid or a

solid changes directly into gas.

4. (a) Iodine

(b) Ammonium chloride

(c ) Solid carbon dioxide

Activity 3

1. (a) P

(b) C

(c) P

(d) C

(e) C


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2. (a) Condensing of water vapour ( or steam) to water as a liquid

(b) Drying or evaporation of water from a salt solution

subsequently collecting back the salt again.

(c ) Freezing of water to ice

3. (a) In a physical change no new substance is formed while in a

chemical change a new substance is formed.

(b) A physical change is reversible while a chemical

change is not.

Activity 4

1. Magnesium

2. Aluminium

3. Zinc

4. Iron

5. Lead

6. Copper

(b) Magnesium + water Magnesium hydroxide +

hydrogen

(c) Hydrogen gas

(d) It puts off a burning split with a pop sound.

Activity 5

1. (a) Acidified water or dilute hydrochloric acid dissolves in

water.

(b) Electrolysis

(c) Oxygen

(d) It puts off a burning splint with a pop sound

(e) Test tube B

(f) Production of strong flame for welding metals or

respiration or for use in incubators in hospitals and deep

water divers


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Activity 6

1. A mixture of solute and solvent

2. Solute

3. Crystallisation4. Saturated solution

Glossary

Alkaline solution: A solution that turns a red litmus paper blue.

Anode: Positive electrode.

Boiling point: The temperature at which a liquid changes to

gas state.

Cathode: Negative electrode.

Chemical change: A change which is not reversible and in which

a new substance is formed.

Chemical reaction: A change in which one or more new

substances are formed.

Electrode: Any conducting material where current

enters or leaves an electrolyte during

electrolysis.

Filtrate: The liquid that passes through a filter.

Mass: Amount of matter contained in a substance.

Physical change: A change in which no new substance is

formed and it is also easily reversed.

Residue: The solid left on a filter paper after filtration.

Temperature: How hot or cold a substance is.

Thermometer: An instrument used to measure temperature.

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Grade8 Science